Multiple-input multiple output (MIMO) systems deploy multiple antennas at either end of a communication link and can provide significant benefits compared to traditional single antenna systems, such as increased data rates through spatial multiplexing gain, and/or improved link reliability through diversity techniques. Recently, the natural extension of utilising multiple antennas in relay networks, known as MIMO relaying, has attracted significant research attention due to the fact that the benefits of MIMO can be coupled with extended network coverage through the use of relaying devices. This thesis concentrates on the design and analysis of different aspects of MIMO relay systems communicating over frequency selective channels with the use of orthogonal frequency division multiplexing (OFDM). The first focus of this thesis is on the development of training based channel estimation algorithms for two-hop MIMO OFDM relaying. In the first phase of channel ...

Joint precoding and equalisation can help to effectively exploit the advantages of multi-input multi-output (MIMO) wireless communications systems. For broadband MIMO channels with channel state information (CSI) such techniques to date rely on block transmission where guard intervals are applied to mitigate inter-block (IBI) and inter-symbol interference (ISI) but reduce spectral efficiency. Therefore, this thesis investigates novel MIMO transceiver designs to improve the transmission rate and error performance. Firstly, a broadband MIMO precoding and equalisation design is proposed which combines a recently proposed broadband singular value decomposition (BSVD) algorithm for MIMO decoupling with conventional block transmission techniques to address the remaining broadband SISO subchannels. It is demonstrated that the BSVD helps not only to remove co-channel interference within a MIMO channel, but also reduces ISI at a very small loss in channel energy, leading to an improved error performance and ...

Multi-input multi-output (MIMO) channels are known to increase the capacity of a transmission link. This can be exploited to increase either the multiplexing gain or the diversity gain, which leads to a higher data throughput or a better resilience of the link to fading, respectively. This thesis is concerned with the diversity gain, which, in a flat fading channel, can be maximised by Alamouti’s space-time block coding (STBC) scheme and a number of derivative techniques. For frequency selective fading, i.e. dispersive, MIMO channels, a few solutions have been reported in the literature including MIMO-OFDM, where the channel is decomposed into a number of narrowband problems, and a technique known as time-reversal STBC. For the latter, a number of blind adaptive algorithms have been derived, implemented and tested in order to avoid the requirement of explicit knowledge of the channel. The ...

In the last decade, one of the most significant technological developments that led to the new broadband wireless generation is the communication via multiple-input multiple-output (MIMO) systems. MIMO technologies have been adopted by many wireless standards such as Long Term Evolution (LTE), Wordlwide interoperability for Microwave Access (WiMAX) and Wireless Local Area Network (WLAN). This is mainly due to their ability to increase the maximum transmission rates, together with the achieved reliability and coverage of current wireless communications, all without the need for additional bandwidth nor transmit power. Nevertheless, the advantages provided by MIMO systems come at the expense of a substantial increase in the cost to deploy multiple antennas and also in the receiver complexity, which has a major impact on the power consumption. Therefore, the design of low-complexity receivers is an important issue which is tackled throughout this ...

Multiple-input multiple-output (MIMO) systems are encountered for example in communications if several transmit and receive antennas are empoyed, such that a separate transmit channel exists between every possible pairing of transmitter and receiver antennas. As a results if this spatial diversity, the channel capacity is dramatically increased over the single-inout single-output (SISO) case. While this increase is desired, the use of high data rates requires sophistiocated equalisation and/or detection schemes in the receiver to compensate for spatial and temporal dispersion in broadband MIMO channels, since a time-dispersive, in addition ot spatially-dispersice channel, must be assumed. The estimation of the broadband MIMO channel or its inverse is in general difficult and calls for training sequences that reduce the slot time for the transmission of actual data, which may counteract the promised gain in channel capacity. Another problem can be the computational ...

Direct-sequence code-divisionmultiple-access (DS-CDMA) and multiple-input multiple-output (MIMO) wireless networks form the physical layer of the current generation of mobile networks and are anticipated to play a key role in the next generation of mobile networks. The improvements in capacity, data-rates and robustness that these networks provide come at the cost of increasingly complex interference suppression and resource allocation. Consequently, efficient approaches to these tasks are essential if the current rate of progression in mobile technology is to be sustained. In this thesis, linear minimum mean-square error (MMSE) techniques for interference suppression and resource allocation in DS-CDMA and cooperative MIMO networks are considered and a set of novel and efficient algorithms proposed. Firstly, set-membership (SM) reduced-rank techniques for interference suppression in DS-CDMA systems are investigated. The principals of SM filtering are applied to the adaptation of the projection matrix and reduced-rank ...

Currently, the telecommunications market has brought changes to the design of the old model of the telecommunications network. The emergence of new technologies for higher speed access was inevitable in order to meet the requirements of the appearance of the multimedia services (VoD, online gaming etc.). The latest technologies for broadband access over telephone pairs are Digital Subscriber Lines or DSL. This set of xDSL technologies allow the transfer of binary high speed over telephone twisted pair by using a suitable type of line codes. They allow a flow of high-speed information both asymmetrical and symmetrical over the telephone loop. This thesis presents the state of the art of Dynamic Spectrum Management (DSM) technologies suggested to improve the performance of DSL systems and proposes a new approach to this issue. The main contributions of this thesis includes extended bandwidth channel ...

When data is transmitted over the wireless communication channel, the transmit signal experiences distortion depending on the channel¢s fading characteristics. On the one hand, this calls for efficient processing at the receiver to mitigate the detrimental effects of the channel and maximize data throughput. On the other hand, the diversity inherently present in these channels can be leveraged with appropriate transmit processing in order to increase the reliability of the transmission link. Recently, in [1] it was shown that the channel characteristics can be exploited to maximize the total data throughput in the interference channel where multiple user pairs rely on the same resource to communicate among themselves. In this PhD dissertation, we first propose novel equalizer designs for frequency selective channels. We then present new results on the diversity gain of equalizers in fading channels when appropriate precoding is ...

When the transmitter of a communication system disposes of some Channel State Information (CSI), it is possible to design linear precoders that optimally allocate the power inducing high gains either in terms of capacity or in terms of reliable communications. In practical scenarios, this channel knowledge is not perfect and thus the transmitted signal suffers from the mismatch between the CSI at the transmitter and the real channel. In that context, this thesis deals with two different, but related, topics: the design of a feasible transmitter channel tracker for time varying channels, and the design of optimal linear precoders robust to imperfect channel estimates. The first part of the thesis proposes the design of a channel tracker that provides an accurate CSI at the transmitter by means of a low capacity feedback link. Historically, those schemes have been criticized because ...

In Broadband Wireless Access systems the efficient use of the resources is crucial from many points of views. From the operator point of view, the bandwidth is a scarce, valuable, and expensive resource which must be exploited in an efficient manner while the Quality of Service (QoS) provided to the users is guaranteed. On the other hand, a tight delay and link quality constraints are imposed on each data flow hence the user experiences the same quality as in fixed networks. During the last few years many techniques have been developed in order to increase the spectral efficiency and the throughput. Among them, the use of multiple antennas at the transmitter and the receiver (exploiting spatial multiplexing) with the joint optimization of the medium access control layer and the physical layer parameters. In this Ph.D. thesis, different adaptive techniques for ...

In recent years, we have assisted to the dawn of many wireless and wireline communication technologies that have adopted multi-carrier modulation (MCM) at the physical layer. The basic idea ofMCMs is to transmit a high rate data stream by dividing it into low rate streams that are used to generate low rate signals each modulated at a given carrier frequency. The use ofMCMs allows for dividing the frequency selective channel into a set of narrow-band sub-channels. Consequently, the transmitted signal experiences, in each sub-channel, a quasi flat frequency response, so that, the equalization task simplifies to a sub-channel filtering. In addition to the simplification of the equalization task, there are several benefits deriving from the use of MCMs that, in general, depend upon the considered transmission medium. The most important ones are the low complexity digital implementation, and the possibility ...

Cooperative communications and multiple-input multiple-output (MIMO) communication systems are important topics in current research that will play key roles in the future of wireless networks and standards. These techniques can provide gains in data throughput, network capacity, coverage, outage, reduced error rates and power consumption, but can have an increased cost in computational complexity and present new problems in many areas. In this thesis, the various challenges in accurately detecting and estimating data signals and allocating resources in the cooperative systems are investigated. Firstly, we propose a cross-layer design strategy that consists of a cooperative maximum likelihood (ML) detector operating in conjunction with link selection for a cooperative MIMO network. The cooperative ML detector is derived, with considerations and approximations made for the knowledge of the system information that is available to the detector. Link selection in the cooperative network ...

The third generation mobile system Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA) has been mainly specified to provide various multimedia capabilities and good service quality. However, since UMTS is based on direct sequence CDMA (DS-CDMA) techniques the performance and the capacity of such systems is significantly limited by multiuser access interference (MAI) and inter-symbol interference (ISI). Therefore, robust and reliable detectors are required to mitigate these effects. Specifically, the multi-user detector exhibits a significant improvement in capacity and spectrum efficiency compared with the conventional matched filter receiver and single-user detector. Nevertheless, its complexity and prior knowledge requirement render it unsuitable for application in the downlink due to handset constraints. In this thesis, we propose a new robust and simple blind multiuser equaliser for downlink DS-CDMA systems, the so-called filtered-R multiple error CM algorithm (FIRMER-CMA) equaliser. The latter has ...

Multiple-input multiple-output (MIMO) systems will be applied in wireless communications in order to increase the performance, spectral efficiency, and reliability. Theoretically, the channel capacity of those systems grows linearly with the number of transmit and receive antennas. An important performance metric beneath capacity is the normalised mean square error (MSE) under the assumption of optimal linear reception. Clearly, both performance measures depend on the properties of the MIMO channel as well as on the considered system approach, e.g. on the type of channel state information which is available at the transmitter. It has been shown that even partial CSI at the transmitter can increase the performance. In this thesis, we analyse the performance and design optimal transmit strategies of singleand multiuser MIMO systems with respect to the statistical properties of the fading channel and under different types of CSI at ...

This thesis proposes different methods to reduce the computational complexity as well as increasing the adaptation rate of adaptive broadband beamformers. This is performed exemplarily for the generalised sidelobe canceller (GSC) structure. The GSC is an alternative implementation of the linearly constrained minimum variance beamformer, which can utilise well-known adaptive filtering algorithms, such as the least mean square (LMS) or the recursive least squares (RLS) to perform unconstrained adaptive optimisation. A direct DFT implementation, by which broadband signals are decomposed into frequency bins and processed by independent narrowband beamforming algorithms, is thought to be computationally optimum. However, this setup fail to converge to the time domain minimum mean square error (MMSE) if signal components are not aligned to frequency bins, resulting in a large worst case error. To mitigate this problem of the so-called independent frequency bin (IFB) processor, overlap-save ...